1. Technical Field of the Invention
The present invention relates to systems for utilizing power generated by solar panels, and more particularly, to an improved electrical connector for use in a modularized photovoltaic system. The invention provides an electrical connector for quickly and efficiently connecting a fully integrated and self-contained alternating current (“AC”) photovoltaic (“PV”) solar panel device to an electrical conductor line that allows photovoltaic applications to become true plug-and-use devices.
2. Description of the Related Art
Most of today's solar photovoltaic (PV) power sources are utility connected. About 75% of these installations are residential rooftop systems with less than 2 kW capability. These systems typically comprise a number of PV modules arranged in series configuration to supply a power converter, commonly called an inverter, which changes the direct current (DC) from the modules to alternating current (AC) to match the local electrical utility supply.
The following U.S. patents relate generally to the state of the art in photovoltaic systems U.S. Pat. No. 6,219,623, to Wills; U.S. Pat. No. 6,285,572 to Onizuka; U.S. Pat. No. 6,201,180 to Meyer; U.S. Pat. No. 6,143,582 to Vu; U.S. Pat. No. 6,111,189 to Garvison; U.S. Pat. No. 6,046,400 to Drummer; U.S. Pat. No. 5,730,495 to Barone; and U.S. Pat. No. 5,702,963 to Vu.
In the case of a single module system producing AC power output, the photovoltaic module is connected to the inverter or load through a junction box that incorporates a fuse to protect the photovoltaic module if backfeeding from other sources (e.g., a power utility or a battery) is possible. The photovoltaic modules used in these systems are configured either with a frame or without a frame. Frameless photovoltaic modules are generally referred to as a laminate. For conventional systems that utilize multiple laminates or modules, the laminates or modules are interconnected via junction boxes or flying leads and external wiring that must be rated sunlight resistant and sized to carry the rated currents. Some conventional photovoltaic system installations require that the direct current (“DC”) and AC wiring be installed in properly sized and anchored conduit.
A typical method of interconnecting the DC circuits in a conventional photovoltaic system is to have a J-box at the top of each photovoltaic module that provides the terminal block to connect the module circuit to flying-lead conductors that are then fitted with a connector. The J-box also houses the series or “blocking” diode often required by codes and standards to protect the module, especially if more than two strings of modules are paralleled at the combiner box or at the inverter. The module is often constructed with a bypass diode(s) that is (are) usually required for conventional photovoltaic applications. This arrangement is used to connect modules in series. Modules are connected in series until the summed operating voltage is within the optimum DC voltage window of the central or string inverter. The connections are typically made under the modules by plugging connectors together or at distributed junction boxes. Some installations leave insufficient space to allow the installer to make the connections reliably. The central inverter can generally handle multiple strings of photovoltaic modules that are then wired in parallel in a string-combiner assembly or box before DC power is fed to the inverter.
The installation of such a system is quite complicated and typically requires the services of a licensed electrician or certified solar installer. A typical installation usually requires the following steps: 1) attaching a support rack to the roof; 2) attaching solar panel arrays to the support rack; 3) adding a circuit breaker to the main electrical system; 4) adding an electrical line from main electrical panel external to AC disconnect; 5) adding an electrical line from AC disconnect to inverter; 6) adding an electrical line from inverter to DC disconnect; 7) adding an electrical line from DC disconnect to combiner box; 8) adding an electrical line from the combiner box to the roof; 9) adding an electrical line to the first and last solar panel array in the string; and 10) adding electrical connections between the solar panel arrays. Typically, all electrical connections in such systems are manually spliced by removing the insulation from each wire to form a proper electrical connection before reinsulating the joined wires.
There is also a difficulty with small solar power systems on residential rooftops. Gables and multiple roof angles make it difficult on some houses to obtain enough area having the same exposure angle to the sun for a system of 2 kW. A similar problem arises where trees or gables shadow one portion of an array, but not another. In these cases the DC output of the series string of modules is reduced to the lowest current available from any cell in the entire string. This occurs because the PV array is a constant current source unlike the electric utility, which is a constant voltage source.
An inverter that economically links each PV module to the utility grid can solve these problems as the current limitation will then exist only on the module that is shaded, or at a less efficient angle and does not spread to other fully illuminated modules. This arrangement can increase total array output by as much as two times for some configurations. Such a combination of a single module and a micro-inverter is referred to as a PV AC module. The AC output of the micro-inverter will be a constant-current AC source that permits additional units to be added in parallel.
While a variety of proposals directed at PV AC modules have previously been made, none have includes a simple efficient means for connecting to the utility grid. Prior art models of PV AC modules suffer poor reliability owing to early failure of the electrolytic capacitors that are used to store the solar cell energy before it is converted to AC. The capacitor aging is a direct consequence of the high temperature inherent in rooftop installations. Moreover, such PV AC modules do not include a simple and efficient means for connection to the utility grid. A need, therefore, exists for an improved and more efficient method and apparatus for safely connecting such PV AC modules to the electrical utility grid.